Porous metal article and method of making same



v Fatented ec. 5, 1939 POROUS BET Willi F. Boil 2 TIGLE METHOD or .rs

a Walter Waleke, and John A.

lliutz, Detroit, Mich, assignors of fifty-one per cent to said Lats, twenty-four and one-half per cent to said man, and twentyf half mr cent to said Walehe and onehlo Drawing. Application @ctober 2d, 1938.

This invention relates to porous metallic artiales and the method of making the same.

For a great many years certain metal articles have been made by mixing together certain alloyable metals each in powder form and first forming them under pressure in dies into a. briquette of approximate shape desired and subsequently heating this briquette and thus alloying the metals to form a finished article. most common example of such an article is the lgironze bearing formed by alloying. copper and I].

It is common knowledge that a metallic article made by the methods in use for years'is porous but only to a limited degree. But more recently a bearing with a more marked porous structure has been considered advantageoin for use as a lubricant retaining medium. This porous requirement has resulted in the development of various methods for increasing the number of voids left in the metal structure, thereby rendering the bearing capable of absorbing and retaming a considerable amount of lubricant. In

general this result has been accomplished by adding Various commercially manufactured organic compounds to the powdered mixture which so co-act on heating of the article as to leave voids in the metal structure which still remain at the termination ofthe heating period.

One of the most important requirements in the manufacture of porous bearings is the formation of a uniform and finely divided porous structure,,as obviously a coarse structure or uneven distribution of voids in the material will not produce satisfactory results, either from the standpoint of absorbing and retaining lubricant or from the standpoint of bearing efiiciency. One disadvantage which has been noted with previous methods is the tendency of the ingredients to flow together to form relatively large masses during the initial heating and therefore to leave large openings in the finished bearing. Such a tendency toward segregation of material added for the purpose of increasing the porous structure $5 sometimes results in a large percentage of socalled scrap in the manufacture of this'type dered metal mixture and which material will The.

powdered may be conveniently added to the powassist in producing the desired uniform porous structure.

' For the purpose of clearly disclosing the practical application of the method or process used to accomplish the improved result of a porous 5 article of uniform structure the following descrip-' tion is given of a method which has been iound to be satisfactory for use in the manufacture of small bronze bearings.

Although the proportion of ingredients varies it? slightly depending upon the degree of porosity desired, it has been found that the following mixture of powdered materials produces a bearing capable of absorbing 16 to 18% of oil by volume.

Per cent by weight Copper 87 Tin 10 Soy bean meal 1 m Graphite 1 Bor l.

The above materials, all in powdered form, are thoroughly mixed in a tumbler unit of a type well known in the art, the tumbler rotating slowly preferably at about 18 to 21 revolutions per minute. I

It is noted that soy bean meal is included in the above mixture, and it is this ingredient which is largely responsible for the establishment of a porous structure in the bearing. lit is worthy of note that soy bean meal provides a material of vegetable origin with a finely distributed oil content. In fact, as is true of vegetable substances in their natural state, the ingredients in the soy bean meal are all carried in a finely divided and what might be termed suspended state with the I granules of meal assuringirelatively uniform distribution of the ingredients thruout the powdered metal mixture. In other words the soy bean meal is a natural vehicle for distributing the ingredients which it carries uniformly thru the powdered metal mixture. It has been found that soy bean meal with a natural oil content of approximately 18% is excellently suited for this purpose although meal of less oil content is practical for use.

After the powdered material has been thoroughly mixed it is then formed into briquettes by the use of pressure and suitable dies in a manner similar to that generally employed in the manufacture of bronze bearings. In this form the briquette is of the approximate shape of the finished bearing, with allowance for a final machining operation after heat treatment. It is important to consider in connection with the new-process here disclosed that the soy been will meal with its finely divided and evenly distributed oil content serves as a very efficient lubricant for the'dies during the forming of the briquettes.

After the bearings are formed as above outlined into briquettes, the next step in the process is the heat treatment to alloy the metals to form the metal structure of the bearing into its finished form. In actual practice of the present process the bearings in the briquette form are preferably initially heated for a period of from 2 to 3 minutes at a temperature, of 900 to 1100 F. This heating is most efiiciently accomplished in a furnace of the type employing a continuous conveyor which carries the bearings to be heat treated through an oven compartment which is heated to the temperature desired. In an installation which has been in actual use the 'aforementioned 2 to 3 minutes, at 900 to 1100 F. is.v

maintained during a three foot travel of the conveyor. The furnace is so arranged around the conveyor unit that after the 3 foot length above mentioned the conveyor then travels into a region where the temperature of 1540" to 1560 F. is maintained for a distance of about four feet and at the speed the conveyor is operated in the installation actually in use, this results in holding the bearings at the 1540 to 1560 temperature for a period of 5 to 6 minutes. It is understood variations in the above outline specific method of heating may be made without departing from the fundamental idea of an initial heat ing followed by a final heating at a higher temperature. It is obvious on consideration that articles of different weight and size will require different timing in the heat cycle to produce equivalent results. For instance, the initial heating above referred to may be satisfactorily accomplished in some instances by simply feeding the articles into a furnace whose central heating region is a constant temperature, the fact that a certain period of time is required to bring a body of metal to a given heat, being sufficient to allow the desired reactions to take place. It may be said therefore that the method is not limited to any specific heat cycle as long as there is an initial heating period sufilcient to allow the desired reactions to take place and in some cases this initial interval may be very short and accomplished in the minimum time required to bring the body of metal under treatment up to the final heat treatment or alloying temperature.

when soy bean meal is employed in the mixture for forming the briquettesand the method carried out as above outlined, there isa definite result obtained during the initial heating period which is primarily responsible for the establishment of a uniform porous structure for the hearing. This result is an immediate tendency of the soy bean material, on heating, to be forced toward the surface of the metal structure. It is to be emphasized that because of the fact that the ingredients in the soy bean material which tend to force their way outward on heating are uniformly distributed and suspended in the cell structure there is no tendency for the ingredients to form large globules on initial heating but rather there is an immediate tendency to be forced outwardly thru the metal thereby estab-' lishing a'uniform and finely divided porous metal structure. In fact it is possible by observation during the initial heating period to note the soy bean material forming on the outer surface ofthe article, the material distributing itself uniformly after establishing small and uniform openings in the metal as it is forced therefrom. It is estimated that approximately 80% of the soy vehicle in which itis suspended in a finely divided state. However in the case of the soy bean the material added is not completely volatile since the ingredients are held in the cellular structure of the soy bean meal in such a perfectly divided state as only nature can de-- vise and being carried by the granules of the meal can be evenly distributed thru the powdered metal mixture. Furthermore although this even distribution is accomplished, the fact thatthe oil together with other ingredients is held in the cellular'structure of the meal the tendency of the particles to form large globules on heating is minimized and consequently part of the soy bean ingredients are driven off by heat in a finely divided state and therefore establish a fine structure of small openings in the metal as previously mentioned and a small residue remains as ash in the metal structure. This small residue of ash in the interstices between the metal particles is also of material value in aiding the absorption and retention of oil by the bearing.

After the initial heating period wherein a major portion, but not all, of the soy bean material is forced to the outer surfaces of the bearing, or other article, the next step in the heat treatment as above noted provides a higher temperature which completes the alloying of the metals and further completes the burning of the soy bean material leaving a uniform porous metal structure, with a small ash residue as aforesaid, capable of absorbing a maximum amount of inbricant without material detriment to the physical properties of the metal which make it suitable for use as a bearing.

After the heat treatment is completed the hearing, or other article, may be machined to size in the usual manner.

Although the process disclosed above employs soy bean meal and the experiments carried out have indicated that this material gives excellent results, it is to be emphasized that other materials of vegetable origin in which the necessary ingredients in correct proportions are held suspended in a natural cellular structure, might give nearly equivalent results. Although soy bean meal has been found by us to give very excellent results we do not desire to limit ourselves entirely to this material but rather to the broad principles of employing a material of vegetable origin having the necessary ingredients carried in the cellular structure thereof and as indicated by the scope of the following claims.

We claim:

1. The method of making porous metal articles which comprises the mixing in powdered form of two or more alloyable metals and adding to and mixing with said alloyable metals a quadtity of powdered material of vegetable origin havbe forced outwardly to the surfaces of said briquette thereby establishing a uniform porous structure for the metal article and subsequently heating-said briquette to a temperature sufiicient to complete the alloying of said metals.

2. The method of making porous metal articles which comprises the mixing in powdered form of two or more alloyable metals and mixing with said alloyable metals a quantity of soy bean meal, subsequently forming said powdered metals and soy bean meal into a briquette of the approximate form desired, and heating said briquettes first at a temperature which will cause a major portion of said soy bean material to be forced outwardly to the surfaces of said briquette thereby establishing uniform porous structure for the metal article and subsequently heating said briquette to a temperature suiiicient to complete the alloying of said metals.

3. A method of mamng porous metal articles of the type wherein powdered metals compressed to approximate shape desired are heated to a temperature suflicient to alloy said metals characterized by the addition to the initial powdered mixture of a powdered material of vegetable origin having a natural oil content held in a finely divided state in the cellular structure of said vegetable material whereby said material is forced to the outer surfaces of said metal article during the initial heating thereof to a degree and for a time sumcient to allow said powdered material of vegetable origin to establish a uniform porous structure in said article.

4. The method of making porous metal articles which comprises the mixing in powdered form of the materials in the following proportions, by weight,

' Per cent Copper 8'? Tin i0 Soy bean meal 1 Graphite i Borax 1 then compressing the mmture into the approximate. form of the article desired and subsequently heating said formed article first at a temperature of from 900 to 1100" F. and subsequently at a temperature-of from 1540 to 1560 F.

5. The method or making porous metal articles which comprises the mixing in powdered form of materials in the following proportions, by weight,

Per cent 37 10 Boy bean meal i Graphite i B01 1 Copper then compressing the mixture into the approximate form of the article desired and subsequently heating said formed aridcle to a degree and for a v time suflicient to allow the formation of a porous structure and to alloy said metals.

6. A method of making porous metal articles of the type wherein metals are compressed in dies to approximate shape desired and are subsequently heated to a temperature sufficient to alloy said metals characterized by the addition to the initial powderedmixture of a powdered material of vegetable origin having a natural oil content held in a finely divided state in the cellular structure of said vegetable material and to alloy said metals.

8. A porous metal article comprising two or more metals alloyed to provide a fine grained uniformly homogeneous structure in which the intersticesbetween the grains contain residual ash of a powdered material of vegetable origin formed when said vegetable powdered material having a natural oil content held in a finely divided state in the cellular structure thereof, uniformly distributed in a powdered mixture of said metals is heated to a degree and for a time sufiicient to allow said vegetable powdered material to assist in establishing a uniform 'porous struc ture in said article and to alloy said metals.

9. A method of making porous metal articles of the type wherein powdered metals compressed to approximate shape desired are heated to a temperature suficient to alloy said metals characterized by the addition to the initial powdered mixture of soy bean meal whereby ingredients in said soy bean meal are forced to the outer surfaces of said metal article during the initial heating thereof to a degree and for a time suficient to allow said soy bean meal ingredients to establish a uniform porous structure in said arhcle. 

